The invention relates to illuminating apparatus in general, and more particularly to improvements in illuminating apparatus of the type described in commonly owned Swiss Pat. No. 627 252 granted Dec. 31, 1981.
The illuminating apparatus which is described in the Swiss patent comprises a light source and an optical system which divides light issuing from the source into a plurality of beams and directs the light beams against the surface which is to be illuminated. The arrangement is such that several light beams impinge upon each unit area of the surface to be illuminated and that discrete luminant spots are observable at the light directing or emitting side of the optical system. The light source is an incandescent lamp, and the optical system comprises a plurality of discrete reflectors. Each reflector is configurated and dimensioned in such a way that the reflected light illuminates the entire surface to be illuminated. An observer of the optical system see the image of the light source in each individual reflector; however, the intensity of light which is reflected by each reflector is merely a minute fraction of the intensity of light issuing from the source, namely a fraction of the overall light intensity (such fraction equals the overall intensity divided by the number of individual reflectors). The just discussed reduction of light intensity is intended to reduce the likelihood of glare.
The patented illuminating apparatus is quite satisfactory when the area of the surface to be illuminated (and hence of the volume of the space which requires illumination) does not exceed a predetermined value. However, the patented apparatus is less effective for illumination of large surfaces and areas, such as uncovered outdoors surfaces or large halls of the type erected in assembly, manufacturing and other plants. The reason is that the intensity of light does not suffice to ensure adequate illumination. If the intensity or brightness of light which is emitted by the light source is increased (an undertaking which is readily achievable by resorting to recently developed types of light sources), the aforediscussed desirable and advantageous effect of reduced light intensity of the image of light source in the reflector is eliminated and the observer of the optical system detects pronounced glare.
In setting up an effective illuminating apparatus, the designer must take into consideration a plurality of important parameters. One of these parameters is the distance of the apparatus from the surface to be illuminated; such distance must be selected with a view to ensure that the apparatus furnishes requisite amounts of light to achieve a desirable brightness. The required brightness will depend upon a variety of factors. For example, if the apparatus is to illuminate the interior of a hall in an assembly plant or in a manufacturing plant wherein the assembly work or manufacturing work must be visually inspected, the required brightness is much more pronounced than when the apparatus is to illuminate a large outdoor area such as a parking area or a railroad freight yard. It is further necessary to take into consideration that the eyes of persons in the area to be illuminated are not always located at the level of the surface to be illuminated. This will be readily appreciated by assuming that the surface to be illuminated is that of a floor. The illuminating apparatus is installed at a level above the floor so that the eyes of persons walking on the floor are disposed at a distance of approximately 1.5-2 meters from (above) the illuminated surface, i.e., nearer to the illuminating apparatus than the floor. The problems which arise due to the difference between the distance of the illuminating apparatus from the illuminated surface on the one hand and the distance of the illuminating apparatus from the eyes of the persons working in the area above the illuminated surface are much more acute if the difference exceeds or greatly exceeds the aforediscussed distance of 1.5-2 meters. This is the situation when one or more persons must occupy the mobile cabin of a crane or a like machine which can move the cabin to or from a level well above the floor or when one or more persons must occupy a conveyance or a platform which is installed at a level above the floor Analogously, the eye of a person who occupies the driver's seat of a truck or a like large vehicle is located at a distance of approximately three meters above the road surface, i.e., much closer to the apparatus which illuminates the road. In order to adequately solve the just discussed problems, it is necessary to design the illuminating apparatus by full consideration of the distance of the eye or eyes of one or more persons from the surface which is to be illuminated. Such persons are those who are in position to accidentally or intentionally look at the illuminating apparatus and who are to be shielded from glare.
Shielding of the eyes of persons who happen to or must occupy illuminated areas is an important problem, i.e., glare should be avoided in order to enable the persons to function properly and to avoid accidents or damage to their eyes. At the same time, the illuminating apparatus must ensure that the area which is to be illuminated is sufficiently bright. As a rule, a person will detect and will be inconvenienced by glare when certain parts of the illuminating apparatus, such as the light source, the reflectors or their holders and certain reflecting objects (such as metallic parts, white surfaces or a wet floor covering) are much brighter to the observer than their surroundings.